1. Field of Invention
The invention relates to a rear projection screen and an optical device thereof and, in particular, to a rear projection screen and an optical device thereof, which can prevent the moiré effect.
2. Related Art
Rear projection televisions are generally applied to television teaching and training of real-sight simulation for pilots and drivers. However, with raising the living standards and improving the living conditions, the rear projection television becomes more and more favor to consumers. Rear projection television is characterized by its wide screen and clear image. Comparing with the conventional cathode ray tube (CRT) television, the rear projection television has the advantages of low irradiation and large screen dimensions, and can connect directly to the computer or other video apparatuses for achieving the maximum of entertainment effects. Therefore, it can be predicted that the rear projection television will play a major role in the market of the entertainment display in the future. In the rear projection television, the image is projected onto the real projection screen from rear side of the screen, and the viewers can obtain the image from the front side of the screen. As a result, there has been a demand for considering that the viewing angles, image contrast, image resolution, and image brightness and so on while one designs the rear projection television.
With reference to FIG. 1, a conventional rear projection screen 1, which is composed of a Fresnel lens 11 and a lenticular lens 12, is a transmissive screen. The Fresnel lens 11 can facilitate to properly utilize light within the visual area so as to raise the brightness and uniformity of image. The lenticular lens 12 is used to generate the image.
The lenticular lens 12 has a plurality of cylindrical convexes 121 formed on the light-incident surface and a plurality of black stripes 122 formed on the light-emitting surface. The incident light beams from the light source are focused in the Fresnel lens 11 and passed away as the parallel light beams, which are incident into the cylindrical convexes 121 later and are further focused. The black stripes 122 made of the light-blocking material are accurately formed in positions corresponding to non-focusing parts of the cylindrical convexes 121. The black stripes 122 formed on the light-emitting surface are used to absorb the light beams for reducing the interference of the outside light.
Generally, a plurality of the black stripes 122 disposed on the cylindrical lens 12 is manufactured as the following description. Coating a photoresist on a surface of the cylindrical lens 12, on which the black stripes 122 are to be formed. Next, the cylindrical convexes 121 is irradiated with light beams from a light source, so that the light beams can be focused with the cylindrical lens 12 on the photoresist. Then, the black stripes 122 is formed by positive development (or negative development) procedures. As the cylindrical convexes 121 are arranged regularly and have approximately the same curvatures and heights, the manufactured black stripes 122 are regular arranged and have the same widths. This may easily cause the interference effect, resulting in the so-called moiré phenomenon that reduces the quality of the image.
Therefore, it is a subjective of the invention to provide a rear projection screen and an optical device thereof, which relieve the moiré phenomenon of the conventional rear projection screen.